This invention concerns a percussion drill or hammer drill.
During drilling, a percussion or hammer drill, also known as a masonry, concrete or stone drill, performs a percussive movement along the drilling axis and a rotary movement about the drilling axis. Both components of its movement contribute to the removal of material in the drill hole. The axial movement shatters the material in the drill hole. The rotary movement, by abrasion, causes a reduction of the material into drilling dust and carries the drilling dust away out of the drill hole.
Known percussion or hammer drills consist of a drill shaft with a hardened metal plate, the cutting plate, set in it. Spiral grooves run along the shaft to evacuate the drilling dust from the drill hole. The cutting plate extends across the diameter of the drill shaft. At its exposed front surface, chip surfaces and free surfaces arranged in a wedge shape form cutting edges. These consist of two linear main edges offset parallel to a plane in which the drilling axis lies, and a transverse edge linking the two main edges through the drilling axis. In order to achieve satisfactory centering when starting to drill, there is an angle not exceeding 130° between the two main cutting edges.